Adsorption powder for removing mercury from high temperature, high moisture gas streams

ABSTRACT

There is disclosed an adsorption powder effective for capturing mercury from a high temperature. high moisture gas stream comprising: about 1-97 % carbon; about 1-97 % of alkaline material about 1-97 % cupric chloride, and about 1-60 % carbon impiegnated with K13. Additionally, a method of removing mercury from high temperature. high moisture gas streams, using the adsorption powder of the invention is disclosed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to removal of pollutantsfrom high temperature, high moisture gas streams such as those found indevices designed to treat contaminated soil and in hazardous materialincinerators. More particularly, the invention relates to the capture ofmercury and other metals, dioxins, furans and other organic compoundsfrom high temperature, high moisture gas streams using an adsorptionpowder containing cupric chloride.

[0002] Strict standards exist for particulate and total mercuryemissions by coal-fired power plants, petroleum refineries, chemicalrefineries, coal fired furnaces, trash burning facilities, incinerators,metallurgical operations, thermal treatment units and other particulateand mercury emitting facilities. These same restrictions apply tomercury vapor, which can enter the atmosphere as a result of lowtemperature thermal desorption (LTTD) treatment of contaminated soils.

[0003] These stringent standards exist in order to protect theenvironment and the community. When mercury-containing gases arereleased, the gases disperse and mercury is deposited over a wide area.The dispersed mercury can accumulate in the soil or water supplies,where it may be incorporated into the food chain. Mercury is extremelyharmful to aquatic life and ultimately to the humans who consumemercury-contaminated plants and animals. It is necessary, therefore, tohave a safe and effective method of eliminating mercury from theenvironment.

[0004] The problem of the capture and treatment of mercury vapor,typically in the context of coal-fired power plants and wasteincinerators, has been previously considered. For example, U.S. PatentNo. 3,193,987 discloses passing mercury- containing vapor over activatedcarbon impregnated with a metal which forms an amalgam with mercury.U.S. Patent No. 4,094,777 discloses passing a mercury- containing vaporover an adsorption mass consisting essentially of a support, sulfidedcopper and sulfided silver. U.S. Patent No. 3,876,393 discloses passingmercury- containing vapors over activated carbon that has beenimpregnated with sulfuric acid. Selenium has also been used in theremoval of mercury from a vapor. U.S. Patent No. 3,786,619 disclosespassing a mercury-containing gas over a mass containing as an activecomponent, selenium, selenium sulfide or other selenium compounds.Electrostatic precipitators and various filters have traditionally beenused for mercury removal, although complex apparatus have also beendisclosed. (See e.g., U.S. Patent Nos. 5,409,522 and 5,607,496.)

[0005] The problem of recapturing mercury from power plant gas streamsis analogous to the need for recapturing mercury from incinerators thattreat contaminated soils. A process currently in use at soil treatmentfacilities is known as low temperature thermal desorption (LTTD). LTTDis the main process by which :contaminated soils are treated to removemercury and other contaminants. In this process, contaminated soils arefed into a heating furnace, most commonly a rotary kiln/drum, where thesoil is heated by conduction. The heating volatizes the soil componentsand when a thermal oxidizer is added, the components are oxidized tomanageable gases, such as CO₂, Cl₂, NO_(x) and SO_(x), where x is 1-3.

[0006] The hot gas stream is subsequently cooled. The stream may bequenched with water, which cools the stream and concurrently increasesthe moisture content. Although water quenching is a highly effectivecooling method, this treatment increases the difficulty of removingmercury from the gas stream. The gas stream is further treated to reduceand remove metals, HCl, NO_(x) and SO_(x) using acid scrubbers, carbonbeds, condensation units and through the addition of adsorption powders.

[0007] When adsorption powders are injected into the gas stream, mercuryand other metals bind to moieties present in the powder, precipitatingthem from the gas stream. The powder-bound mercury is ultimatelycollected in a bag house for appropriate disposal, while the clean gasstream is exhausted to the outside atmosphere. The problem with standardLTTD methods is that some metals, such as mercury, are not removed fromthe stream at high efficiency and will move with the gas stream,ultimately into the environment. Other methods require the use ofcomplex machinery and expensive adsorption beds. LTTD and other methodsalso suffer from the limitation that mercury removal from high moisturegas streams is much more difficult than mercury removal from drystreams.

[0008] Available adsorption powders remove organics, metals and othercontaminants, but they do not effectively remove mercury. For example,one available powder (Sorbalite™) consisting of carbon, calciumhydroxide and sulfur removes HCl from a gas stream, but it removed onlyabout 55-65% of the mercury. Another powder (WUELFRAsorb-C™) consistingof alcohol saturated lime and activated carbon is also inefficient atremoving mercury.

[0009] Some powders include sulfur or iodine impregnated carbon. Attemperatures of 75° C. or less, sulfur or iodine impregnated carbonbased powders show a 95% mercury removal efficiency, however, powdersformulated with sulfur impregnated carbon require that the gas stream towhich they are added is dry.

[0010] Lastly, the mercury removal efficiency of the powders describedand other available powders is known to be very temperature dependent,placing an additional limitation on powder formulations.

[0011] Accordingly, there is a need in the industry for an adsorptionpowder that effectively removes metals and other organic compounds, ingeneral, and mercury, in particular, from high temperature, highmoisture gas streams generated by the incineration of contaminatedsoils, treatment of hazardous materials, combustion of coal and othermercury liberating sources. The powder must be inexpensive and easy touse. Ideally, such an adsorption powder can be employed at treatmentfacilities already in place and can take advantage of equipment alreadyin position, without requiring retooling or reconfiguring existingequipment.

SUMMARY OF THE INVENTION

[0012] There is disclosed an adsorption powder and method for removingmercury and other metals and contaminants from a high temperature, highmoisture gas stream comprising: about 1-97% carbon; about 1-97% calciumhydroxide; about 1-97% cupric chloride and about 1-60% KI₃ impregnatedcarbon. A method for removing mercury and other metals, dioxins, furansand other organic compounds from high temperature, high moisture gasstreams using the claimed powder is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The instant invention will be more fully understood in thefollowing detailed description, it being understood, however, that theinvention is not confined to the precise disclosure. Changes andmodifications may be made that do not affect the spirit of theinvention, nor exceed the scope thereof, as expressed in the appendedclaims. Accordingly, the instant invention will now be described withparticular reference to the accompanying drawings.

[0014]FIG. 1 is a schematic diagram illustrating the design of an LTTDfacility in which the claimed adsorption powder can be used to removemercury from gas streams.

DETAILED DESCRIPTION OF THE INVENTION

[0015] There is disclosed an adsorption powder for removing mercury andother metals from a gas stream comprising:

[0016] a) about 1-97% carbon;

[0017] b) about 1-97% calcium hydroxide;

[0018] c) about 1-97% cupric chloride; and

[0019] d) about 1-60% KI₃ impregnated carbon.

[0020] In a preferred embodiment, there is disclosed an adsorptionpowder for removing mercury and other metals from a gas streamcomprising about 30% coal carbon, about 50% calcium hydroxide, about 10%cupric chloride and about 10% KI3 impregnated carbon.

[0021] There is also disclosed a process for removing mercury from a gasstream using the adsorption powder of the invention comprising the stepsof:

[0022] a) placing a solid phase mercury-containing contaminated soilfeed into a rotary kiln/drum;

[0023] b) heating said kiln/drum containing said soil feed to formgaseous and solid components of the sample;

[0024] c) transferring the gaseous component of said soil feed to anexhaust cleaning unit/afterburner and the solid component of clean soilto a soil cooling unit;

[0025] d) heating the gaseous component of said contaminated soil feedin said exhaust cleaning unit/afterburner;

[0026] e) cooling the gaseous component of said contaminated soil feed;

[0027] f) adding the adsorption powder of claim 1 to the gaseouscomponent;

[0028] g) transferring the powder-containing gaseous component to abaghouse; and

[0029] h) releasing the substantially mercury-free gaseous component ofsaid sample to the atmosphere.

[0030] An adsorption powder for the removal of mercury and other metals,dioxins, furans and other organic compounds must be efficient under arange of conditions. Currently available powders do not function well athigh temperatures and in high moisture environments, conditions that arefavorable to mercury removal.

[0031] High temperatures are necessary for effective removal ofcontaminants from soil. Temperatures of about 1800° F. are necessary tovolatize organics, metals and other impurities from the contaminatedsoil. Mercury that is trapped in contaminated soil, however, is mostefficiently adsorbed on carbon at about 300-500° F. The most practicalmethod of cooling a gas stream exiting an 1800° F. oven is to injectwater into the gas stream. Water injection cools the gas stream to atemperature favorable to mercury removal, but also increases themoisture content of the sample, which decreases the efficiency ofavailable mercury adsorption powders. The mercury absorbing propertiesof available powders suffer dramatically in a high moisture environment.The adsorption powder of the invention, however, operates effectivelyeven in a higher moisture environment.

[0032] Experiments with carbon sources showed that coal carbon wassuperior to wood carbon for mercury adsorption. Many availableadsorption powders use wood carbon as a component, rather than coalcarbon. Cupric chloride was observed to significantly enhance theadsorption of mercury from a gas stream and is the key to the instantinvention. Cupric chloride supplies chlorine and activated copper to theelemental mercury in the exhaust stream. Elemental mercury reacts withthe chlorine to form mercury chloride and the activated copper to form astable mercury amalgam. Both forms of mercury are easily captured fromthe exhaust gas stream. KI₃ impregnated carbon was also found toincrease mercury adsorption when it was included in the powder.

[0033]FIG. 1 shows a schematic diagram of the actual process andequipment used to carry out the invention. Prescreened contaminated feedsoil ready to be processed 2 is placed within soil cleaning unit 4. Thecontaminated soil is heated to about 900° F. or a temperature that willcompletely volatize the contaminates from the soil and generate a gasstream, as well as a clean/remediated solid soil component. Preferably,soil cleaning unit 4 is a rotary kiln. The gas stream is then passed outof soil cleaning unit 4 to dust remover 6, while any solid fraction ofthe feed soil is transferred to clean soil cooling unit 8, where thesoil is cooled and prepared for reuse. Dust remover 6 is preferably amulti-tube dust collector.

[0034] After dust remover 6 removes any particulate matter from the gasstream sample, the gas stream is passed into the Exhaust Cleaning Unit10. The Exhaust Cleaning Unit heats the volatilized contaminates to atemperature of about 1800° F for a minimum of two seconds retentiontime, which assures complete destruction of any remaining organic orother contaminants. From the Exhaust Cleaning Unit 10, the gas streamthen passes through cooling chamber 12 wherein a water pump (not shown)injects water into the cooling chamber 12 to lower the temperature ofthe sample to about 360° F. This cooling process consequentiallyincreases the moisture content of the sample.

[0035] The high temperature, high moisture gas stream is then contactedto the adsorption powder of the invention, which is stored in adsorbentstorage silo 14 and injected into the gas stream. This powderformulation is effective in removing metals, particularly mercury, andother contaminants.

[0036] After the gas stream has been contacted to the adsorption powder,the powder/gas stream mixture continues on to baghouse 16. The carboncomponent of the adsorption powder collects on the walls of bags andacts as a particulate filter for the gases leaving the baghouse.Baghouse 16 collects the particulate mercury-containing fraction of theadsorption powder mixture, which is transported to a suitable bulkstorage facility 20 and subsequently removed. The gaseous fraction isreleased to the outside atmosphere through vent 18, while the remainingdust particulate fraction is handled in a similar manner to theparticulate mercury fraction of the adsorption powder mixture 20.

EXAMPLE 1

[0037] A series of field tests were performed employing a preferredadsorption powder formulation. Three soil samples containing about 4.2mg/kg of mercury were prepared by screening to 1 inch. The coarsematerial was discarded, and the remaining soil was fed into a soilcleaning unit and heated to about 900° F. The cleaned soil wastransferred to a soil cooling unit and prepared for reuse. The exhauststream was sent to a dust remover and the precipitated material was sentto the soil cooling unit.

[0038] The exhaust stream was then fed into an exhaust cleaning unit,which was heated to about 1850° F. The exhaust gas was then cooled toabout 360° F. by quenching with water, and subsequently an adsorptionpowder comprising 30% coal carbon, 10% KI₃ impregnated carbon, 50%calcium hydroxide and 10% cupric chloride was added.

[0039] The exhaust stream/adsorption powder mixture was fed into abaghouse, where the mercury-bound particulate was separated from themercury-free exhaust gas. The particulate material was removed from thebaghouse for analysis and disposal, while gas analyzers on the exhauststack recorded mercury emission levels. The results of the three, twohour runs are reported in the following table. Run 1 Run 2 Run 3 AverageLTTD Mercury Input (lbs/hr) 0.193 0.199 0.199 0.197 Clean Soil MercuryOutput (lbs/hr) 0.0020 0.0020 0.0020 0.0020 Mercury Emission Rate(lbs/hr) 0.0012 0.0006 0.0007 0.0008 Mercury Removal Efficiency¹ 99.4%99.7% 99.6% 99.6%

[0040] The average mercury removal efficiency of 99.6% exceeds thecurrent mercury control efficiency specification of 96.5% efficiency,set by NJDEP air permit legislation. Mercury emissions were determinedby EPA method 29-060.

[0041] Although the adsorption powder and method described and claimedare presented in the context of mercury removal from a gas stream, itshould be appreciated that the powder and method are also useful forremoving organics, metals and other contaminants from a gas stream.

What is claimed is:
 1. An adsorption powder for removing mercury andother metals, dioxins, furans and other organic compounds from a gasstream comprising: a) about 1-97% carbon; b) about 1-97% calciumhydroxide; c) about 1-97% cupric chloride; and d) about 1-60% K₁₃impregnated carbon.
 2. The adsorption powder of claim 1 wherein theadsorption powder comprises about 10-70% carbon, about 20-80% calciumhydroxide, about 1-50% cupric chloride and about 1-50% KI₃ impregnatedcarbon.
 3. The adsorption powder of claim 1 wherein the adsorptionpowder comprises about 20-60% carbon, about 30-70% calcium hydroxide,about 1-30% cupric chloride and about -30% KI₃ impregnated carbon. 4.The adsorption powder of claim 1 wherein the adsorption powder comprisesabout 25-45% carbon, about 40-60% calcium hydroxide, about 1-15 % cupricchloride and about 1-15 % KI3 impregnated carbon.
 5. The adsorptionpowder of claim 1 wherein the adsorption powder comprises about 30%carbon, about 50% calcium hydroxide, about 10% cupric chloride and about10% KI3 impregnated carbon.
 6. The adsorption powder of claim 1 whereinthe carbon is coal carbon.
 7. A method for removing mercury and othermetals, dioxins, furans and other organic compounds from a gas streamusing the adsorption powder of claim 1 comprising the steps of: a)placing a solid phase mercury-containing contaminated soil feed into arotary kiln/drum; b) heating said kiln/drum containing said soil feed toform gaseous and solid components of the sample; c) transferring thegaseous component of said soil feed to an exhaust cleaningunit/afterburner and the solid component of clean soil to a soil coolingunit; d) heating the gaseous component of said contaminated soil feed insaid exhaust cleaning unit/afterburner; e) cooling the gaseous componentof said contaminated soil feed; f) adding the adsorption powder of claim1 to the gaseous component; g) transferring the powder-containinggaseous component to a baghouse; and h) releasing the substantiallymercury-free gaseous component of said sample to the atmosphere.
 8. Amethod of claim 7 wherein the adsorption powder used in step f)comprises about 30% carbon, about 50% calcium hydroxide, about 10%cupric chloride and about 10% KI₃ impregnated carbon.